Means for voltage regulation in alternating current supplies



R. I. BAG NALL Feb. 7, 1933.

MEANS FOR VOLTAGE REGULATION IN ALTERNATING CURRENT SUPPLIES Filed May1, 1931 ji/Cijii CCCC C fA/k/N 2 v gm (42M ii/Mfg? rulZZ v 3)". D DNYiii/i22 (CCCC C between the load circuit and Patented Feb. 7, 1933UNITED STATES PATENT OFFICE.

ROBERT IBONBIDI BAGNALL, LONDON, ENGLAND m FOB VOLTAGE IN ALTEBNATIN GCURRENT SUPPLIES Application and m 1, 19:1,

This invention relates to voltage regulatsystems for alternating currentsupplies of the kind wherein use is made of reactors g windingsconnected between the load circuit and separate tappings on the windof atransformer.

ith such regulating systems hitherto known it has been necessary toemploy separate magnetizing windings on the reactors and somewhatcomplicated electrical means externally for varying the current in themagnetizing windings and thereby the inductances of the reactors inorder to attain the desired voltage regulating efi'ects.

Now the resent invention has for its object to provide an improvedmethod and simplified means for of voltage in alternating current ischaracterized primarily by the automatic regulation supplies and theemployment of choke coils of dissimilar electro magnetic characteristicsmakin connection t e tappings upon the transformer winding.

According to this invention use is made of simple choke coils ofdissimilar electro-magnetic characteristics connected between the loadcircuit and the tappings on the transformer windin and operatingautomatically m a manner w arlses from the ereby the voltage regulationeffect of the choke coils and transformer alone.

e improved regulating system may according to design be arrang agecharacteristic ed to give a voltwhich uses, or falls or is approximatelyconstant with increasin current and is'therefore es the for ially suitabe for ose of overcoming or compensating rop in voltage which may occurwith increasing load in cables, transformer and the like.

In carryin effect as for t e the invention into practical purpose ofcompensating the voltage drop arising in cables and transformer windingsuse is made of a transformer having tappmgs capable of giving electricalpressures above and below that required in the consumption circuit whichis connected on the one hand directly to one end of the transformerwindi through the two di 11 and on the other hand ssimilar chokes to thetaplerlal in; 534,501, and in Great Britain an a, 1930.

pings on the transformer winding. In the example under consideration thechoke coil connected to the tapping point of excessive pressurepreferably has a closed circuit core which saturates at relatively lowcurrent values whilst the other choke coil connected to the tappingpoint of lower electrical pres sure possesses a lower magneticinduction, its core preferably being gapped or discontinuous in order toassist in procuring the required characteristic. The two choke coils maybe regarded as arranged in series and bridged across the tappings of thetransformenthe gotential of the load circuit being determined y thevoltage existing-at the point common to the two choke coils. At no load,the choke of high induction, absorbs a certain part of the pressurebetween the tappings but as the current increases the voltage of thechoke of low magnetic induction increases more rapidly than the voltageof the choke of high induotlon by an amount which ma be arranged tocompensate for the drop of pressure occurring in the cables andtransformer windms The invention is hereinafter more fully describedwith reference to the accompanyin drawing wherein ig. 1 shows diarammatically an example of the improve; voltage regulating system with adouble wound transformer;

Figs. 2 and 3 are diagrammatic views of "difi'erent forms of chokecoils;

Figs. 4 and 5 are respectively front and side elevation illustrating achoke coil of 35 variable magnetic induction.

Fig. 6 is a diagram illustrating a modified arrangement of the voltageregulating system with an auto-transformer.

Fig. 7 shows diagrammatically a further form of choke coil of variablemagnetic induction.

Referring to Figure 1 the apparatus shown comprises a double woundtransformer 1 having a primary winding 2 with terminals 3 adapted to beconnected with a source of supply of alternating current (not shown) anda secondary windin 4 whose full pressure between the termina s 5 and 6at no load exceeds that required in the load 9 below that required inthe load circuit. The

system also includes two choke coils whose windings 8 and are connectedat one end I nated iron core 9 forming a closed magnetic.

to the terminal 6 and the tappings7 respectively and at the other end toone feeder 12 for the load circuit. The other feeder 13 for the loadcircuit is connected to-the terminal 5 .of the transformer winding.

The choke coil 8 is provided with a lamicircuit, whilst the choke coil10 is preferably provided with a core 11 of gapped or discontinuousform. The exact design of the cores and windings ofthechoke coil willdepend on such factors as the amount and nature of the load to be dealtwith and the amount of voltage drop to be compensated between no loadand full load conditions.

It will be seen that the two windings 8 and 10 are connected in serieswith one another to points 6 and 7 of the transformer secondary coil, sothat when the transformer primary is energized and no current consumingdevice is connected to the outgoing terminals 12 and 13 a current willass through the choke coil windings, and t e voltage measured betweenterminals 6 and 7 will be divided between the two coils 8 and 10 to adegree depending. principally on the relative inductance of the twochoke coils at that current. The choke coils are so designed andproportioned and the tapping point 7 and full pressure at the terminal 6are so ar ranged that the voltage then obtained between terminals 12 and13 is that which it is desired to supply from the outgoing terminalswhen no load is connected to them, and

in this condition neither of the choke coil cores should be saturatedmagnetically, and the current passing through their coils shouldpreferably be as small as possible compared with the maximum currentrequired by the consuming devices consistent with satisfactory operatingcharacteristicsv of the a paratus at varyin loads.

The clloke coil 8 is ma e so that a lar e increase in current requires arelatively sma 1 increase in voltage across the choke coil terminals.This is secured by using a suitable value of induction or density ofmagnetization in the core. The choke coil 10 on the other hand is madeso that a greater proportional increase in voltage is required at its-terminals when an increased current passes.

through its windings than is the case with choke coil 8, and to obtainthis result the core may be worked at a lower induction than that usedin the core of choke coil'8 when considered in reference to the no loadcondition an air gap in the magnetic circuit assists in obtaining thisresult. Although the cores of these choke coils are described as beingconstructed of iron, it ,7

is to be understood that other materia/Is such as alloys having suitablecharacterist'cs be used instead, and the exact "value of induction intheir magnetic circuits especially of choke coil 8 will depend on themagnetic characteristics of the material used for the cores.,

When a load in the form of'a currentcon; suming device is connected tothe outgoin terminals 12 and 13 increased current wi pass throughwinding 8 causing an increase in voltage' across the terminals 6 and 12.

The method of operation will be best understood if considered inrelation to a load of a nature as to have approximately unity powerfactor, in which case a considerable angle will exist between the vectorof its voltage and the vector of the voltage across the terminals ofchoke coil 8. There will then be an increase also in voltage at theterminals of the choke coil 10 and therefore the current through chokecoil 10 will be increased.

By suitable design these respective increases in voltage on the twochoke coils may be so arranged to ensure that the'voltage obtainedbetween the outgoing terminals 12 and 13 will increase as the loadconnected to them is increased up to a point representing the fullcapacity of the apparatus, there-- by compensating approximately at allvalues the voltage drop occurring in the conductors.

It may here be mentioned that the transformer employed may be of anyordinary commercial form and although as illustrated diagrammatically inFigure 1 it is shown as having primary and secondary windings onseparate limbs it would be made in accordance with usual and well knownpractice so as to be-efiicient and convenient for its purpose;

Furthermore the choke coil 8 may be of any convenient form; Thus itswindings may be mounted on a core of closed rectangular form as shown inFigure 1 or the laminated core may be ofannular form as shown in Figure2 or of the shell type indicated in Figure 3.

The core 11 of the choke coil 10 may be constructed with a fixed or anadjustable air gap. Figures 4 and 5 show a form of 0011-:

struction wherein the core comprises a main portion 14 composed oflaminations bolted or otherwise suitably held together, and a similarlyconstructed yoke portion 15. The winding of the choke coil surrounds oneof the limbs of the main portion 14 of the core and yoke 15 is connectedto the niain portion of the coil by distance bolts 16 in a mannerpermitting the air gap between the parts to be adjusted for the purposeof varying the electro-magnetic characteristics of the choke coil. 1

Figure 6 shows diagrammatically a voltageregulating system which isprecisely similar to that described with reference to I Figure 1 exceptthat it is provided with an nected to the tapping point of lowerpressure auto-transformer instead wound transformer. winding isconnected by appropriate tappings with the source of supply and alsowith the load circuit and the regulating choke coils.

In some conditions it may be desirable to use as an alternative to theform of choke coil 10 indicated in Figure 1 a construction in which theiron core or some part of it is supported so as to be capable ofmovement under the control of a weight or spring. One

form of this construction is shown diagrammatically in Figure 7 where 17is the coil winding and 18 the core, which is suspended partly withinthe coil by the spring 19 from a support 20. Means may be provided foradjusting the initial position of the core such as a stop 21 and foradjusting the tension of the spring such as a screwed stem and nuts orthe like 22.

These parts are adjusted so that as the current passing through the coilincreases when load is connected to the terminals 12 and 13 the core isattracted further into the coil thus increasing the inductance of thechoke coil.

Although in the foregoing description the application of the improvedvoltage regulating system to single phase supplies only is considered itshould be understood that the regulating system is equally adaptable tomulti-phase supplies. Thus for example in a three-phase supply threeregulating systems arranged as described might have their transformerswindings star connected whereupon 'the regulated three-phase supplywould be available at the points of connection between the choke coils.

Having now particularly described my invention what I claim as new anddesire to protect by Letters Patent is 1. Means for the automaticregulation of voltage in alternating current supplies comprising asupply transformer having tappings giving pressures respectively aboveand slow a predetermined normal pressure in a load circuit, a choke coilhaving permanent high electro-magnet induction characteristics connectedbetween the high pressure tapping and the load circuit and a choke coilof permanent lower electro-magnetic induction characteristic connectedbetween the low pressure tapping and the load circuit, said circuitmagnetic core, and the choke coil conof with a double is constructedwith a gapped or discontinuous In this case the same core.

